The present invention relates to a shift control system used for a vehicular automatic transmission comprising a shift lever, which is manipulated by a driver.
A vehicular automatic transmission is designed to perform automatic speed control for a vehicle on the basis of the following conditions: the position of the shift lever, which is manipulated by the driver at the driver""s seat of the vehicle; the movement of the accelerator pedal being stepped down by the driver in relation with the respective drive range determined by the position of the shift lever; the speed of the vehicle, etc. The drive ranges which can be selected by the manipulation of the shift lever are, for example, a parking range (P range), a reverse drive range (R range), a neutral range (N range), and a forward drive range (e.g., D range, etc.), and in many cases, the forward drive range comprises, for example, D range, S range, xe2x80x9c2xe2x80x9d range and xe2x80x9c1xe2x80x9d range. For the selection of these ranges, generally, the shift lever is swiveled in a plane appropriately to select respective drive ranges. In this case, a shift guide path is provided linearly in a form of slot at the driver""s seat, and the shift lever, which extends through the shift guide path, is manipulated along the guide path by the driver for the selection of the drive ranges.
On the basis of this design, shift control systems have been proposed and designed in variation not only to enable the shift lever to swivel linearly along a linear shift guide path but also to allow various patterns of shift manipulation through appropriate arrangement of shift guide paths. For example, Japanese Laid-Open Patent Publication No. H2(1990)-8545 discloses a shift control system with two shift guide paths: a first shift guide path (or first shift path), which is linear as the above described shift guide path, and a second shift guide path provided parallel with this first shift guide path. The manipulation of the shift lever along the first shift guide path enables the selection of the following drive ranges: P, R, N, D, 3, 2 and 1. In this system, when the shift lever is at the position for the D range, it can be moved into the second shift guide path. Then, in the second shift guide path, the shift lever is manipulated for exclusive selection of the D, 3, 2 and 1 ranges.
Also, Japanese Laid-Open Patent Publication No. H6(1994)-221417 discloses a shift control system which allows the shift lever to be manipulated not only linearly in a shift guide path for selection of P, R, N, D and B ranges but also perpendicularly to this shift guide path when the shift lever is at the B range position, for an upshift and a downshift in steps. Furthermore, this patent publication discloses a shift control system in which the shift lever is manipulated along a linear first shift guide path to select P, R, N, D, M and L ranges and is movable laterally at the M range into a second shift guide path, where the shift lever is manipulated for an upshift and a downshift in steps.
Although various types of shift control systems have been proposed as mentioned above, it is generally considered advantageous to differentiate the P range from the other drive ranges. The P range is a range to be set when the engine is not operating. It is usually selected when the vehicle is parked, i.e., when the engine is stopped and the driver leaves the vehicle behind. On the other hand, the other ranges are set while the driver is operating the vehicle at the driver""s seat. There is a significant difference between the condition where the P range is set and the condition where the other ranges are set. Therefore, a shift control system, if it is designed to offer a clear difference in the manipulation of the shift lever for the selection of the P range, is considered to improve the operativity of the shift lever.
It is an object of the present invention to provide a shift control system for a vehicular automatic transmission, which system offers a clear difference in the manipulation of the shift lever so that the driver can differentiate clearly a range for parking (P range) from other drive ranges (for example, R and D ranges).
In order to achieve this objective, the present invention provides a shift control system for a vehicular automatic transmission comprising a shift lever, which is manipulated and translated at least among a parking position, a neutral position, and a selective position. The shift control system is provided with a first shift guide path to guide the shift lever from the parking position (xe2x80x9cPxe2x80x9d position) through the neutral position (xe2x80x9cNxe2x80x9d position) to the selection position (xe2x80x9cSxe2x80x9d position) and a second shift guide path to guide the shift lever which has been positioned at the selection position into a direction different from that of the first shift guide path. In this second shift guide path, the shift lever is shifted appropriately to select and establish a plurality of ranges necessary for driving a vehicle, including a forward drive range, a neutral range and a reverse drive range.
In this shift control system, the shift lever is shifted along the first shift guide path to select the position used for parking (xe2x80x9cPxe2x80x9d position) or the position used for driving (xe2x80x9cSxe2x80x9d position). When the vehicle is driven, the shift lever is shifted along the second shift guide path to select and establish a plurality of drive ranges (D5, D4, D3, 2, 1, etc.). In other words, the range selection for parking the vehicle is executed by the manipulation of the shift lever along the first shift guide path while the range selection for driving the vehicle is executed by the manipulation of the shift lever along the second shift guide path. Therefore, the shift control system according to the present invention provides a good operativity for shift lever manipulation.
This shift control system can be arranged such that when the shift lever is shifted from the neutral position to the selection position in the first shift guide path, the neutral range is established, and then every time when the shift lever is swiveled in the second shift guide path, an appropriate range is selected in a predetermined sequence. With this arrangement, the control of the vehicle flows smoothly from the parking condition to the driving condition because the neutral range is the first range which is selected when the shift lever is shifted from the neutral position to the selection position in the first shift guide path. Furthermore, as the selection of the drive ranges is effected simply by swiveling the shift lever at the selection position along the second shift guide path, the shift control system according to the present invention makes the manipulation of the shift lever during the drive easy and simple.
It is preferable that the shift control system be provided with a vehicle speed sensor which detects the speed of the vehicle and that the system be arranged to prohibit the selection of a first predetermined range (for example, the reverse drive range) even though the shift lever is manipulated along the second shift guide path while the speed of the vehicle detected by the vehicle speed sensor is equal to or higher than a predetermined speed. With this arrangement, even if the driver manipulates the shift lever accidentally in a way to select the reverse range while the vehicle is driving forward, for example, the neutral range can be established for safety instead of the reverse range.
Furthermore, it is also preferable that the shift control system be provided with abnormality detection means for detecting abnormality or a failure in the execution of the range selection performed in response to the manipulation of the shift lever. In this case, the system is preferably arranged such that if a failure is detected by the abnormality detection means, then a second predetermined range can be selected and established automatically when the shift lever is positioned at the selection position. With this arrangement, if a failure or abnormality is detected, the transmission is set, for example, into the xe2x80x9c2xe2x80x9d range as the second predetermined range, and the vehicle in this limited performance can be driven to a garage for repair.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.